Various ceramics such as SiC and Si3N4, which have good properties such as heat-resistance, chemical stability and mechanical strength, have been proposed so far for structural members for aircraft, spacecraft, nuclear reactors, nuclear fusion reactors, power plants which consume fossil fuel, or the like exposed to a severe atmosphere under heavy-duty conditions. Such ceramics are also used as members of heat exchangers or mechanical seals driven under heavy-duty conditions. Especially, SiC is a suitable material in various industrial fields from aerospace to nuclear power generation, due to its excellent heat-, corrosion- and wear-resistance as well as chemical stability and mechanical strength.
SiC is brittle itself, despite of good high-temperature property with a sublimation temperature higher than 2600° C. In order to overcome poor toughness, a SiC fiber-reinforced SiC-martix composite (hereinafter referred to as merely “a SiC composite”) has been proposed, as reported in A. Lacombe and C. Bonnet, 2nd Int. Aerospace Planes Conf. Proc. AIAA-90-5208 (1990) and C. W. Hollenberg et al., J. Nucl. Mat., 219, (1995)70-86.
Several methods, e.g. hot-pressing and liquid-phase sintering, have been developed so far for manufacturing a SiC composite. However, since it is very difficult to manufacture a SiC composite having high mechanical strength and excellent rupture property, the same steps are necessarily repeated in order to improve properties of the SiC composite. Repetition of the same steps complicates a manufacturing process and raises a manufacturing cost. Moreover, members with complicated profiles can not be manufactured with ease due to repetition of the same steps. In this meaning, a SiC composite has not been available for industrial application, yet.
By the way, a liquid-phase sintering method has been proposed, whereby heat-resistant SiC fiber, which has quasi-stoichiometric composition with high crystallinity, is used for reinforcement and a matrix of a SiC composite is formed by liquid-phase sintering. The manufactured SiC composite has a dense structure with excellent thermal conductivity. However, there still remains un-solved problems for well-balancing rupture strength with toughness at high levels.